U.S. patent application number 12/092989 was filed with the patent office on 2008-10-16 for distributing and driving light sources of backlights.
This patent application is currently assigned to KONINKLIJKE PHILIPS ELECTRONICS, N.V.. Invention is credited to Henricus Marie Peeters, Renatus Willem Clemens Van Der Veeken.
Application Number | 20080252591 12/092989 |
Document ID | / |
Family ID | 37708438 |
Filed Date | 2008-10-16 |
United States Patent
Application |
20080252591 |
Kind Code |
A1 |
Peeters; Henricus Marie ; et
al. |
October 16, 2008 |
Distributing and Driving Light Sources of Backlights
Abstract
The present invention relates to a backlight for a display
device comprising at least a first light source arrangement (1) and
a second light source arrangement (2) and drivers for controlling
said light source arrangements. The backlight further comprises a
third light source arrangement (3), wherein each one of the first
and second light source arrangements (1, 2) is controlled by a
respective driver (5, 6) such that luminance of the first and
second light source arrangements (1, 2) are individually
controllable, wherein each of the first and second light source
arrangements (1, 2) is controlled such that luminance profile of
the first and second arrangements (1, 2) is arranged to approximate
at least a portion of a luminance profile of the third light source
arrangement (3).
Inventors: |
Peeters; Henricus Marie;
(Eindhoven, NL) ; Van Der Veeken; Renatus Willem
Clemens; (Eindhoven, NL) |
Correspondence
Address: |
PHILIPS INTELLECTUAL PROPERTY & STANDARDS
P.O. BOX 3001
BRIARCLIFF MANOR
NY
10510
US
|
Assignee: |
KONINKLIJKE PHILIPS ELECTRONICS,
N.V.
EINDHOVEN
NL
|
Family ID: |
37708438 |
Appl. No.: |
12/092989 |
Filed: |
November 3, 2006 |
PCT Filed: |
November 3, 2006 |
PCT NO: |
PCT/IB2006/054079 |
371 Date: |
May 8, 2008 |
Current U.S.
Class: |
345/102 ;
362/234 |
Current CPC
Class: |
G02F 1/1336 20130101;
G02F 1/133604 20130101; G09G 2320/0666 20130101; G02F 1/133603
20130101; G09G 2320/0233 20130101; G09G 3/3413 20130101; G09G 3/342
20130101; G02F 1/133613 20210101; G02F 1/133609 20130101 |
Class at
Publication: |
345/102 ;
362/234 |
International
Class: |
G09G 3/36 20060101
G09G003/36; F21V 33/00 20060101 F21V033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 14, 2005 |
EP |
05110678.9 |
Claims
1. A backlight for a display device comprising at least a first
light source arrangement (1) and a second light source arrangement
(2) and drivers (5, 6) for controlling said first and second light
source arrangements (1, 2), said backlight comprising a third light
source arrangement (3), wherein each of said first and second light
source arrangements (1, 2) is controlled by a respective driver (5,
6) such that luminance of said first and second light source
arrangements (1, 2) is individually controllable, wherein each of
said first and second light source arrangements (1, 2) is arranged
such that luminance profile of said first and second arrangements
(1, 2) is controlled to approximate at least a portion of a
luminance profile of the third light source arrangement (3).
2. The backlight according to claim 1, wherein at least one light
source (A, B, C, D) comprised in said first light source
arrangement (1) is interspersed with light sources comprised in
said second light source arrangement (2), whereby a gradual
luminance transition from said first light source arrangement (1)
to said second light source arrangement (2) is achieved, when said
first light source arrangement (1) is arranged to have a different
luminance than said second light source arrangement (2).
3. The backlight according to claim 2, wherein said at least one
light source (A, B, C, D) is arranged to be located at the
periphery of said first light source arrangement (1).
4. The backlight according to claim 1, wherein said backlight is
divided into zones (A, B, C, D), said first light source
arrangement (1) being arranged to correspond to a first zone (A)
and said second light source arrangement (2) being arranged to
correspond to a second zone (B).
5. The backlight according to claim 4, wherein said at least one
light source (A, B, C, D) is physically located where a portion of
said first zone (A) overlaps a portion of said second zone (B).
6. The backlight according to claim 4, wherein said first zone (A)
is formed as a quadrangle and said second zone (B) is formed as a
quadrangle that surrounds said first zone (A), and said second
light source arrangement (2) is located outside the first zone (A),
in the area enclosed by said quadrangle forming said second zone
(B).
7. The backlight according to claim 1, wherein said third light
source arrangement (3) has a spatial elongation and said first and
second light source arrangements (1, 2) are aligned in a direction
of the spatial elongation of said third light source arrangement
(3).
8. The backlight according to claim 7, wherein a first light source
set (81) comprises a row of light sources from said first light
source arrangement (1), a second light source set (82) comprises a
row of light sources from said second light source arrangement (2),
and a third light source set (83) comprises a row of light sources
of which every other light source is comprised in the first light
source arrangement (1) and every other light source is comprised in
the second light source arrangement (2).
9. The backlight according to claim 8, wherein the sets (81, 82,
83) of light sources are arranged along said direction of
elongation.
10. The backlight according to claim 1, wherein said backlight is
provided with a hexagonal structure (144) of light sources (1, 2,
3, 4, 5) said hexagonal structure (144) comprising at least a first
light source row (141) being displaced in relation to a second
light source row (142) located next to said first row (141), a
third light source row (143) located next to the second row (142)
being displaced in relation to the second row (142) and columns of
said third row (143) being aligned with columns of light sources in
said first row (141).
11. The backlight according to claim 10, wherein said first and
second light source arrangements are arranged in triangular
shapes.
12. The backlight according to claim 1, wherein said backlight
comprises light emitting diodes.
13. The backlight according to claim 1, wherein said backlight
comprises hot cathode fluorescent lamps.
14. A display device comprising the backlight according to claim 1
and a display panel for displaying a picture.
15. Driver means (5, 6) for a backlight of a display device, said
driver means being arranged to control at least a first light
source arrangement (1) and a second light source arrangement (2) of
said backlight, such that luminance of said first and second light
source arrangements (1, 2) is individually controllable and
luminance profile of said first and second light source
arrangements (1, 2) is controlled to approximate at least a portion
of a luminance profile of a third light source arrangement (3).
16. The driver means according to claim 15, wherein said driver
means are arranged to drive at least one light source (A, B, C, D),
comprised in said first light source arrangement (1), said light
source being interspersed with light sources comprised in said
second light source arrangement (2), whereby a gradual luminance
transition from said first light source arrangement (1) to said
second light source arrangement (2) is achieved, when said driver
means are arranged to drive said first light source arrangement (1)
such that is has a different luminance than said second light
source arrangement (2).
17. The driver means according to claim 15, wherein said driver
means comprise a plurality of driver means arranged to control
respective light source arrangements, whereby said backlight is
divided into zones (A, B, C, D), such that a first driver is
arranged to correspond to a first zone (A) and a second driver is
arranged to correspond to a second zone (B).
18. A method of driving a backlight for a display device,
comprising at least a first light source arrangement (1) and a
second light source arrangement (2), said method comprising the
step of: individually controlling the luminance of said first and
second light source arrangements (1, 2) such that luminance profile
of said first and second arrangements (1, 2) is approximating at
least a portion of a luminance profile of a third light source
arrangement (3).
Description
[0001] The present invention relates to a backlight for a display
device comprising at least a first light source arrangement and a
second light source arrangement and drivers for controlling said
light source arrangements. The invention further relates to a
display device comprising the backlight, driver means for a
backlight of a display device and a method of driving a backlight
for a display device.
[0002] A backlight is a light source arrangement that is placed
behind or at a side of a display, such as a liquid crystal display
(LCD), to illuminate the display and make displayed information
visible. A backlight is particularly favorable under poor lighting
conditions. Today, there exist many types of backlights, such as
backlights using white light sources or red/green/blue light
sources. Several different types of light sources are used in
backlights, for example light emitting diodes (LEDs), hot cathode
fluorescent lamps (HCFLs) and cold cathode fluorescent lamps
(CCFLs). Some backlights comprise small light bulbs arranged along
an edge of a display device, and are hence unevenly distributed
over the display. Other backlights may comprise light sources,
which may be evenly distributed over the entire display area.
[0003] Backlights of display devices are, for example, known from
published US patent application US 2002/007091, which discloses a
backlight for an LCD comprising an array of LEDs and LED drive and
control circuitry. The luminance of the backlight is provided by
the array of LEDs. The backlight may be driven and controlled by a
fast pulse power converter, thus providing a response time for the
backlight in the order of microseconds. The backlight may thus, for
instance, be used for displaying images provided by a video signal
input to the LCD. Furthermore, by separately adjusting the average
light output of the red, green and blue LEDs, the color content of
the LED backlight may be varied. The light output (luminance) of
the red, green and blue LEDs may be independently controlled by
separate controllers.
[0004] In published Japanese patent JP2005070228, there is
disclosed a backlight, provided at the rear of a display, which
backlight creates a light emitting surface being composed of a
plurality of areas that illuminate independently of each other. In
this manner, the disclosed backlight provides a blinking technique
capable of eliminating display blurs and flicker. A problem of this
backlight is that luminance profile differences between different
light sources of the backlight interfere with the image being
displayed.
[0005] In a hybrid backlight, combining red LEDs with fluorescent
lamps in green and blue, the differences in luminance profile
between the LEDs and the fluorescent lamps cause color
inhomogeneities. These color inhomogeneities present a disadvantage
of the hybrid backlights.
[0006] An object of the present invention is to reduce color
inhomogeneities associated with hybrid backlights.
[0007] Another object of the present invention is to reduce
differences in luminance profile of different light source
arrangements comprised in a display device backlight.
[0008] These and further objects are met by the device as set forth
in the appended independent claim 1. Specific embodiments are
defined in the dependent claims.
[0009] According to an aspect of the invention, there is provided a
backlight for a display device comprising at least a first light
source arrangement and a second light source arrangement and
drivers for controlling the light source arrangements. The
backlight further comprises a third light source arrangement. Each
one of the first and second light source arrangements is controlled
by a respective driver such that luminance of the first and second
light source arrangements are individually controllable. The first
and second light source arrangements are individually controlled
such that luminance profile of the first and second arrangements
can be approximated with at least a portion of luminance profile of
the third light source arrangement.
[0010] The luminance profile of a light source may be defined as
the luminance of the light source as a function of form and shape
of the light source. For example, the luminance at the center of a
circular (or spherical) light source is usually greater than the
luminance at the periphery of such a light source, i.e. luminance
decreases with increasing radius. Thus, the luminance profile may
be approximated with a function, which is declining from the center
towards the periphery of the light source. Further, the luminance
profile of a set of light sources relates to overall luminance of
the light source set. It should be noted that a light source
arrangement may comprise one single light source as well as a
plurality of light sources. Additionally, an overall luminance
profile of a light source arrangement comprising a plurality of
light sources may be arranged to be controlled such that it
approximates the luminance profile of a light source arrangement
comprising one single light source.
[0011] An idea of the invention is to provide a display device
backlight, which comprises at least a first and a second light
source arrangement comprised in the backlight, such that the first
and second light source arrangements may be controlled to
approximate luminance of a third light source arrangement comprised
in the backlight. Further, the luminance of each light source
arrangement is controlled by means of a separate driver, i.e. each
driver is associated with at least one light source arrangement
comprised in the backlight. The luminance profile of the third
light source arrangement is approximated as follows. Luminance of
the first light source arrangement and the second light source
arrangement are associated with a first and a second portion,
respectively, of the luminance profile of the third light source
arrangement. The luminance of the first light source arrangement
may then be controlled to provide a local approximation of the
first portion of the third light source arrangement. Similarly, the
luminance of the second light source arrangement may be controlled
to provide a local approximation of the second portion of the third
light source arrangement. Consequently, the luminance of the first
and second light source arrangements create an overall luminance
profile, which approximates the luminance profile of the third
light source arrangement. In practice, a large number of light
sources are employed to approximate the luminance profile of a
light source arrangement. For instance, a set of LEDs are employed
to approximate luminance profile of one HCFL.
[0012] In a first embodiment of the invention, the first and the
second light source arrangement comprise a plurality of light
sources, and at least one light source comprised in the first light
source arrangement is interspersed with light sources comprised in
the second light source arrangement, whereby a gradual luminance
transition from the first light source arrangement to the second
light source arrangement is achieved, when the first light source
arrangement is arranged to have different luminance than the second
light source arrangement. Interspersion of the light sources is
employed to blur edges that may occur between light source
arrangements having different luminance. The interspersion provides
a smooth luminance transition between adjacent light source
arrangements, which as above are arranged to have different
luminance. A light source is, for example, considered to be
interspersed with other light sources when all neighboring light
sources belong to one or more other light source arrangements. A
further example of interspersion is, when every other light source
arranged in a row is associated with the first and the second light
source arrangement, respectively. An advantage with the
interspersion implemented in this embodiment is that borders
between light source arrangements are dimmed and a gradual
transition in luminance from one light source arrangement to
another light source arrangement is achieved.
[0013] In a second embodiment, there is provided a display device
backlight, in which the first and second light source arrangements
are arranged to have a first color and the third light source
arrangement is arranged to have a different color than the first
color. Advantageously, the color content of the light emitted by
the backlight for a display device can be controlled by varying the
ratio of light emitted by the first and second light source
arrangement to light emitted by the third light source
arrangement.
[0014] Further, the backlight for a display device is divided into
zones, wherein the first light source arrangement is arranged to
correspond to a first zone and the second light source arrangement
is arranged to correspond to a second zone. The first zone is
formed as a quadrangle, particularly a rectangle, and the second
zone is arranged to be formed as a quadrangle, particularly a
rectangle, that surrounds, the first zone. Preferably, the first
zone is concentric with the second zone. The light sources of the
second zone are hence located outside the first zone, in the area
that is enclosed by the rectangle forming the second zone.
Additionally, the quadrangles may have rounded corners.
Advantageously, this arrangement allows for compensating
differences in luminance profile between two light source
arrangements in the horizontal as well as vertical direction.
[0015] In another embodiment of the backlight for a display device
according to the invention, light sources of the first and second
light source arrangements are arranged in a row. It is advantageous
to arrange the first and the second light source arrangements in a
row when the luminance profile to be matched is extending along the
same row. Further, the row may comprise additional light source
arrangements such that the overall luminance profile of the light
source arrangements is represented by a larger number of local
luminance approximations (each luminance approximation originating
from a separate light source arrangement). In this manner, a more
flexible approximation of the luminance profile of the third light
source arrangement may be achieved.
[0016] Furthermore, each row of light source arrangements or light
sources comprises the same number of light source arrangements or
light sources, whereby the backlight for a display device may be
controlled by a row-column-addressing technique. Advantageously,
each light source or light source arrangement may be controlled by
two parameters (a row dimming factor and a column dimming factor).
The columns in a row have a common row-dimming factor and the
actual luminance profile matching for that row is controlled by the
column dimming factors of each respective column. Hence, the row
dimming factor provides a base luminance level and the column
dimming factors may be varied such that a given luminance profile
can be matched. Since many rows have a similar shape in their
luminance profiles, but may be slightly offset with respect to
their base luminance levels, only the row dimming factors need to
be varied such as to change the base luminance level and the column
dimming factors may be reused. On the other hand, in cases where
rows have the same base luminance level, the row dimming factors
may be reused. In this manner, the size and complexity of the
control electronics may be reduced. The row and column dimming
factors may be stored in a look-up table.
[0017] Additionally, the dimming factors may be controlled by
feedback from a sensor, such as a light or temperature sensor. As
an example, the temperature at the first light source arrangement
may be different from the temperature at the second light source
arrangement. When the luminance profile of the light source
arrangements are affected by the temperature it is not possible to
use a look up table. Instead, the row and column dimming factors
may be controlled by a signal from the temperature sensor.
[0018] Furthermore, light source arrangements that are controlled
to emit light of the same (or similar) luminance (in order to
approximate a given luminance profile) may be connected to the same
driver. As a result, the total number of drivers are reduced.
[0019] Moreover, the light source arrangements may comprise light
emitting diodes (LEDs), hot cathode fluorescent lamps (HCFLs), cold
cathode fluorescent lamps (CCFLs) or a combination thereof. In an
embodiment of the present invention, the backlight for a display
device may be a hybrid backlight, which for instance may comprise
LEDs as well as HCFLs. A hybrid backlight may preferably be used in
combination with an LCD. Advantageously, the backlight for a
display device according to another embodiment of the invention
comprises LEDs and HCFLs, wherein the LEDs are arranged to emit red
light and the HCFLs are arranged to emit green and blue light. With
this configuration, the low power properties of the green and blue
HCFLs are combined with the low power properties of the red LEDs in
a preferred manner. The HCFLs may be located between the LEDs as
described below or, alternatively, the HCFLs may be located on top
of the LEDs.
[0020] Further features of, and advantages with, the present
invention will become apparent when studying the appended claims
and the following description. Those skilled in the art realize
that different features of the present invention may be combined to
create embodiments other than those described in the following,
without departing from the scope of the present invention.
[0021] Further aspects according to the invention relate to a
display device comprising the backlight, driver means for the
backlight of a display device and a method of driving the backlight
for a display device as defined in the claims.
[0022] The various aspects of the invention, including its
particular features and advantages, will be readily understood from
the following detailed description and the accompanying drawings,
in which:
[0023] FIG. 1 shows a luminance profile of a group of LEDs and a
lamp, respectively;
[0024] FIG. 2 is a top view of a backlight being divided into zones
according to an embodiment of the invention;
[0025] FIG. 3 shows a first graph of a luminance profile and a
second graph, which is an approximation of the first graph;
[0026] FIG. 4 shows a backlight, which is divided into zones
according to another embodiment of the invention;
[0027] FIG. 5 is a block diagram, showing control and driver
circuitry for controlling light sources comprised in zones;
[0028] FIG. 6 shows an LED configuration of a backlight according
to an embodiment of the invention;
[0029] FIG. 7 shows an LED configuration of a backlight according
to another embodiment of the invention;
[0030] FIG. 8 shows an LED configuration, in which interspersion is
implemented, of a backlight according to a further embodiment of
the invention;
[0031] FIG. 9 shows two graphs of the luminance of a portion of the
backlight according to the embodiment of FIG. 8.
[0032] FIG. 10 shows an LED configuration, in which interspersion
is implemented, of a backlight according to yet a further
embodiment of the invention; and
[0033] FIG. 11 shows an LED configuration, in which interspersion
is implemented, of a backlight according to another embodiment of
the invention.
[0034] FIG. 12 shows an LED configuration, in which interspersion
is implemented, of a backlight according to a still further
embodiment of the invention;
[0035] FIG. 13 shows an LED configuration, in which interspersion
is implemented, of a backlight according to a further embodiment of
the invention; and
[0036] FIG. 14 shows an LED configuration, in which an
interspersion is implemented, of a backlight according to yet
another embodiment of the invention.
[0037] In FIG. 1, there is illustrated two different luminance
profiles; one (denoted 11) is associated with a group of LEDs that
are arranged in alignment along a given direction and the other
(denoted 12) is associated with a fluorescent lamp such as an HCFL,
which lamp extends in the same given direction and has a length
which is substantially the same as the length of the group of LEDs.
The respective luminance profile is represented by luminance L of
the respective light source (or group of lights sources) as a
function of its spatial extension x in the given direction. In FIG.
1, it can be seen that when moving in the direction of any one of
two end points--i.e. along the spatial extension x--of the group of
LEDs and the lamp, respectively, the luminance profile 11 of the
LEDs deviates from the luminance profile 12 of the lamp. At the
respective end point of the spatially extending lamp, the luminance
decreases, while in the case of the group of LEDs, overall
luminance is relatively constant irrespective of direction of
extension. It can be concluded from FIG. 1 that in the case a
fluorescent lamp is arranged adjacent to a group of LEDs in e.g. a
display backlight, color inhomogeneities (also referred to herein
as "color clouds") appear at a physical location where the
luminance profiles deviate from each other.
[0038] Now referring to FIG. 2, there is shown a top view of a
backlight for a display device according to an embodiment of the
invention. The backlight is divided into zones A, B, C and D. For
each zone A, B, C and D there is one respective driver 1, 2, 3 and
4, which controls the LEDs in the corresponding zone. Further, the
backlight for a display device according to this embodiment
comprises HCFLs, as shown in FIG. 4 and discussed in connection
thereto. In this embodiment of the invention, the zones are
arranged as concentric rectangles, having rounded corners, whereby
the luminance of the LEDs in zones provides an approximation of the
luminance profile from HCFLs, comprised in the display device
backlight. The HCFLs are arranged to emit green and blue light. In
this embodiment, the zones are arranged as concentric rectangles,
having rounded corners, whereby the LEDs in zones provides an
approximation of the luminance profile from the HCFLs.
[0039] In FIG. 3, there is illustrated a first graph 31 of a
luminance profile of a fluorescent lamp. The graph 31 is divided
into portions, wherein each portion corresponds to a respective
zone A, B, C, D or E. Each zone comprises a group of LEDs. Each
group of LEDs can be driven to provide a respective luminance level
32, 33, 34, 35 or 36. Hence, each respective luminance level 32,
33, 34, 35 or 36, corresponding to a respective zone A, B, C, D or
E, provides a local approximation of the corresponding portion of
the luminance profile of the lamp. Consequently, the luminance
levels 32, 33, 34, 35 and 36 create an overall luminance profile,
which approximates the continuous luminance profile of the
lamp.
[0040] In FIG. 4, another example of how the backlight may be
divided into zones is illustrated. Each row, R1, R2, R3, etc., is
divided into a number of columns, and a column may comprise one or
more LEDs. Each zone, which is addressed by means of specifying row
and column, is associated with a respective LED group driver 1, 2
and 3 (all drivers are not shown). Between rows of LEDs R1, R2, R3,
etc., fluorescent lamps 4, 5 are arranged. The fluorescent lamps
may also be located on top of the LEDs (not shown). The fluorescent
lamps 4 are in this particular example green and the fluorescent
lamps 5 are blue. Alternatively, the lamps 4, 5 may be replaced by
one fluorescent lamp, which is arranged to emit blue and green
light. As can be seen in FIG. 4, the number of columns may differ
from one row to another row, but other configurations, such as a
fixed number of columns for each row are also possible to
implement. With the division into zones according to this
particular embodiment, one row of LEDs may be controlled to provide
an overall luminance profile that match the luminance profile of
one lamp 4, 5. The maximum number of zones is calculated as the
maximum number of columns (zones) in one row (m) times the number
of rows (n):
t.sub.max=m.times.n.
[0041] In FIG. 4, rows R1 and R2 are divided into five different
zones, respectively, while row R3 is divided into seven different
zones, each zone comprising one light source or a plurality of
light sources. For full flexibility in matching e.g. the overall
luminance profile of row R1 with the fluorescent lamp 4, each zone
should be driven with its own driver, such that the luminance of a
zone in row R1 can be adjusted independently of any other zone in
row R1.
[0042] Referring to FIG. 5, the control electronics of the
backlight according to an embodiment of the invention is
demonstrated. FIG. 5 shows a lookup table T, a measure and control
unit MC, a row dimming factor R, a column dimming factor C,
feedback FBCK, a LED-group driver L-DR and LEDs L. The LED-group
driver L-DR is connected to one zone. There are additional
LED-group drivers for other zones, but these drivers are not shown.
A dimming factor controlling the luminance of a zone, is controlled
by the row-dimming factor R and the column-dimming factor C. The
columns in a row have a common row-dimming factor and the actual
luminance profile matching for that row is controlled by the column
dimming factors of each respective column. Hence, the row dimming
factor provides a base luminance level and the column dimming
factors vary such as to provide a varying luminance level along the
row, which luminance level matches a given luminance profile. The
feedback FBCK is, in this example, a light sensor signal. Hence,
when the backlight is placed in a dark room the luminance of the
backlight is controlled by means of the signal from the light
sensor to provide a higher luminance.
[0043] Each letter A-F in FIGS. 6-8 and 10-13 denotes one or more
LEDs associated with a respective zone A-F, each zone being driven
by a separate driver. R1, R2, R3 denote the first, second and third
row. For reasons of simplicity, only three rows are
illustrated.
[0044] In FIG. 6, there is shown an LED configuration of a
backlight according to an embodiment of the invention. The
backlight is divided into four vertical zones, each zone comprising
LEDs A, B, C and D respectively. As shown in FIG. 4, fluorescent
lamps may be arranged between the rows R1, R2, R3, etc. such that
there are two HCFLs between row R1 and row R2, and two further
HCFLs between row R2 and row R3. It is preferred to use red LEDs in
combination with blue and green HCFLs. For simplicity, the HCFLs
are not shown in FIG. 6. Again, in an alternative embodiment HCFLs,
emitting blue and green light, are arranged between, on top of or
under the LEDs. All LEDs A can be driven such that the luminance
profile of the LEDs A locally match a corresponding portion of the
luminance profile of the HCFLs. Similarly, the LEDs B, C and D can
be driven such that their respective overall luminance profile
locally match a portion of the luminance profile of the lamp that
corresponds to each zone B, C and D. Hence, the overall luminance
profile of the LEDs A, B, C and D approximates the continuous
luminance profile of the HCFL in the horizontal direction.
[0045] FIG. 7 shows an LED configuration of a backlight according
to another embodiment of the invention, in which the zones
comprising LEDs A, B and C are arranged as concentric rectangles,
which have rounded corners. Again, the HCFLs are omitted for
simplicity. In this embodiment the luminance profile of the HCFLs
is matched in the horizontal as well as the vertical direction.
[0046] In the following, a few examples of interspersion will be
described. In FIG. 8 and FIG. 10 to FIG. 13, the underlined letters
in the figures denote interspersed LEDs.
[0047] In FIG. 8, an interspersion of light sources is shown. The
LED configuration shown in FIG. 8 is described and the HCFLs
illustrated in FIG. 4 are not shown in FIG. 8. However, the HCFLs
can be arranged as shown in FIG. 4. The backlight according to FIG.
8 comprises four zones, whereby a reduction of luminance
differences, in the horizontal direction, between groups of LEDs A,
B, C and D may be achieved. In row R1 a sequence of LEDs A are
followed by a sequence of LEDs, in which every other light emitting
diode is a LED A and every other light emitting diode is a LED B.
This sequence of interspersed LEDs is, in its turn, followed by a
sequence of LEDs B. As a consequence, the sequence of interspersed
LEDs provide a luminance transition from the luminance of the LEDs
A to the luminance of LEDs B (provided that luminance of LEDs A and
B are different). If the luminance profile of an HCFL is symmetric
a further reduction of the number of drivers can be obtained by
connecting LEDs A and LEDs D to the same driver.
[0048] In FIG. 9, there is shown two graphs. The solid line graph
represents a portion of a continuous luminance profile (e.g.
according to FIG. 3) and the dashed line graph illustrates the
luminance from the LEDs A and the LEDs B. The dotted line
demonstrates a gradual luminance transition from luminance of LEDs
A to luminance of LEDs B. In this manner, the differences in
luminance between a first zone comprising LEDs A and a second zone
comprising LEDs B is evened out.
[0049] Referring to FIG. 10, there is shown an interspersion
strategy, in which the LED configuration is different for different
rows R1, R2, R3, etc. The LEDs of row R2 are slightly displaced in
relation to the LEDs of row R1. Further, the LEDs of row R3 are
displaced in relation to the LEDs of row R2 and so forth. Hence,
the LEDs are arranged diagonally over the display device backlight.
As in the other examples, the HCFLs are not shown. This
configuration is suitable if the luminance profiles of the HCFLs
are different for different rows.
[0050] The embodiment of FIG. 11 is similar to that of FIG. 7 in
that horizontal and vertical luminance defects are compensated for.
However, in FIG. 11 interspersion is implemented such as to reduce
luminance differences from LEDs of different zones.
[0051] FIG. 12 is yet a further example of interspersion. In this
example, LEDs belonging to more than two zones are interspersed. In
this embodiment, the sequence of interspersed LEDs comprises LEDs
from as many as four different zones of LEDs A, B, C and D. By way
of arranging the light sources in this manner, the luminance
transition between zones may be made even smoother than in
previously described embodiments. The degree of smoothing of the
luminance transition depends on a number of factors, such as the
spacing between the LEDs, the radiation profile of the individual
LEDs and the overall optics employed in the display device
backlight.
[0052] Obviously, a combination of the interspersion strategy in
FIGS. 11 and 12 would yield yet a further example of
interspersion.
[0053] Moreover, in FIG. 13, yet another example of interspersion
is shown. In this example, LEDs from an arbitrary number of zones
are interspersed in order to further smoothen the luminance
transition from one zone to another. By combining a larger number
of zones, a further reduction of the number of drivers needed may
be achieved. This can be done by combining zones of two or more
rows, but also by combining two zones in the same row. For example,
A1 could be combined with F1, B1 with E1, and C1 with D1. This
would create a symmetrical light distribution and less drivers per
row would be needed.
[0054] In FIG. 14, there is shown an LED configuration, in which a
hexagonal structure provides two-dimensional interspersion. A
hexagonal structure may be provided by means of arranging the light
sources in rows, which rows are arranged such that a first row is
slightly displaced in relation to a second row following the first
row. Further, a third row following the second row may be displaced
in relation to the second row and so on. Columns of the third row
are aligned with columns of the first row. Hence, two light sources
of the first row, three light sources of the second row and two
light sources of the third row may form a hexagonal structure. A
minimum of three rows are required to create a hexagonal structure.
In FIG. 14, the distribution for a single LED color is shown. The
reference numerals 1-7 denote one zone, respectively (i.e. a total
of seven zones), each zone having a substantially triangular shape.
Due to the hexagonal structure, every LED has six neighbors, which
advantageously enables an even light distribution.
[0055] In a further example, the backlight according to an
embodiment of the invention comprises red, green and blue LEDs. The
red LEDs are arranged according to a first LED configuration and
the blue LEDs are arranged according to a second LED configuration,
i.e. zones comprising red LEDs and zones comprising blue LEDs must
not coincide. The green LEDs may, of course, be arranged according
to a third LED configuration. Thus, zones comprising LEDs of
different colors are independently arranged.
[0056] A man skilled in the art realizes that many other examples
of interspersion of light sources may be implemented to provide an
approximation of a luminance profile.
[0057] Even though the invention has been described with reference
to specific exemplifying embodiments thereof, many different
alterations, modifications and the like will become apparent for
those skilled in the art. The described embodiments are therefore
not intended to limit the scope of the invention, as defined by the
appended claims.
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